In recent years, automotive vehicles, such as recreational four-wheel drive vehicles, have becoming increasingly sophisticated in terms of the type and number of electrical accessories which are either fitted to the vehicle as original equipment manufacturer (OEM) items or installed as after market accessories. For example, four-wheel drive vehicles may be fitted with HF radios, winches, refrigerators, GPS navigational systems, and high powered external lights. Although such accessories (or loads) are not usually essential to the operation of the vehicle, they nevertheless increase the electrical load which is placed on the primary electrical power source of the vehicle, and may require electrical power to operate when the vehicle is not operating.
In a conventional automotive vehicle, the primary source of electrical power may include a single lead-acid battery which supplies power to the vehicle's essential electrical systems (including the starting system) and the accessories. In such circumstances, when the vehicle is not operating, and thus when the battery is not being recharged by the vehicle's battery charging system, operating the accessories may inadvertently drain or discharge the battery and leave insufficient charge for the battery to start the vehicle.
One attempt to provide increased supply capacity involves installing multiple batteries (which may include a main battery and one or more auxiliary batteries) which are connected in a parallel circuit by operating a switch when additional capacity is required for starting the vehicle or operating an accessory. However, such an arrangement requires user intervention and may result in both batteries being discharged if the user fails to disengage the switch after use.
Another attempt to provide increased supply capacity involves providing a battery isolation unit which maintains a main battery and one or more auxiliary batteries in a parallel circuit unless the terminal voltage of the primary battery falls below a predetermined level. If the terminal voltage of primary battery, and thus the charge of the battery, does fall below the predetermined level, the battery isolation unit then operates to isolate the main battery from the electrical load to thereby preserve sufficient charge to start the vehicle. Existing battery isolation units may include a solenoid which incorporates a magnetically operated switch which is held in a closed position by maintaining an inductor or coil in an energised state. In the closed state the switch completes the parallel circuit between the main battery and one or more auxiliary batteries.
Unfortunately, in existing battery isolation units the current (and thus power) required to maintain the inductor or coil in an energised state may contribute to self-heating of the solenoid and thus of the battery isolation unit. In extreme cases, the self-heating may lead to adversely effect the reliability of the battery isolation unit, or at least decrease its service life. In addition, the current required to maintain the inductor or coil in an energised state depletes the available capacity of the battery.
It would be desirable to provide a battery isolation unit which provides reduced self heating effects. It would also be desirable to provide a battery isolation unit which provides a reduced power consumption.